In many industrial processes, undesirable excess heat is removed by the use of heat exchangers in which water is used as the heat exchange fluid. Copper and copper-bearing alloys are often used in the fabrication of such heat exchangers, as well as in other parts in contact with the cooling water, such as pump impellers, stator and valve parts. The cooling fluid is often corrosive towards these metal parts by virtue of containing aggressive ions and by the intentional introduction of oxidizing substances for biological control. The consequences of such corrosion are the loss of metal from the equipment, leading to failure or requiring expensive maintenance, creation of insoluble corrosion product films on the heat exchange surfaces, leading to decreased heat transfer and subsequent loss of productivity, and discharge of copper ions which can then "plate out" on less noble metal surfaces and cause severe galvanic corrosion, a particularly insidious form of corrosion.
Accordingly, it is common practice to introduce corrosion inhibitors into the cooling water. These materials interact with the metal to directly produce a film which is resistant to corrosion, or to indirectly promote formation of protective films by activating the metal surface so as to form stable oxides or other insoluble salts. However, such protective films are not completely stable, but rather are constantly degrading under the influence of aggressive conditions in the cooling water. Under very aggressive aqueous environments, such as those defined as brackish, those containing salt or brine or those containing sulfides, the maintenance of protective films is particularly difficult. The common copper corrosion inhibitors, such as benzotriazole, tolytriazole or mercaptobenzotriazole cannot establish a passive film on the metallic surface under these conditions. This is true even for the exceptional copper corrosion inhibitor, n-butyl benzotriazole. It appears that the copper ions produced at a high rate under these conditions complex with and deactivate the inhibitors. However, if excess inhibitor is used, the result is the undesirable formation of a film consisting of the insoluble copper-inhibitor complex. It is an object of this invention to provide an effective corrosion inhibitor for copper or copper containing surfaces in contact with a very aggressive aqueous environment.